Biology for Kids
What is an organ?
An organ is a group of tissues in a living organism that has a specific form and function.
Organs are grouped together into organ systems. Organ systems perform a specific task. In most animals there are ten major organ systems:
- Nervous system - The nervous system is responsible for carrying messages from the brain to various parts of the body. It includes the brain, spinal cord, and nerves.
- Respiratory system - The respiratory system is responsible for breathing. It transfers oxygen into the blood stream and removes carbon dioxide. It includes the lungs, larynx, and airways.
- Cardiovascular or circulatory system - The cardiovascular system carries blood throughout the body to help bring nutrients to various other organs. It includes the heart, blood, and blood vessels.
- Digestive system - The digestive system processes food into substances that different parts of the body can use for energy and nutrients. It includes organs such as the stomach, gallbladder, intestines, liver, and pancreas.
- Endocrine system - The endocrine system uses hormones to regulate many functions throughout the entire body such as growth, mood, metabolism, and reproduction. Major organs in the endocrine system include glands such as the pituitary, thyroid, and adrenal glands.
- Excretory system - The excretory system helps your body to get rid of food and toxins that it doesn't need. It includes organs such as the kidneys and bladder.
- Integumentary system - The integumentary system protects the body from the outside world. It includes the skin, hair, and nails.
- Muscular system - The muscular system is made up of all the muscles in our bodies. It is controlled by the nervous system.
- Reproductive system - The reproductive system includes all the organs needed for reproduction. Unlike the rest of the organ systems, the reproductive system is different in males versus females.
- Skeletal system - The skeletal system provides support and protection for the rest of the organ systems. It is made up of bones, ligaments, tendons, and cartilage.
Yes, all complex living organisms have some types of organs. The three major organ systems in plants include roots, stems, and leaves. You can go to this page to learn more about the major structures of plants.
Major Organs in the Human Body
As you can see from the long list of organ systems, the human body has a large number of organs that somehow all work together to keep us alive. Here is a list and short description of a few of the major organs.
- Brain - Perhaps the most important organ in our body is the brain. It is here where we think, feel emotions, make decisions, and control the rest of the body. The brain is protected by a thick skull and fluid.
- Lungs - Lungs are major organs that bring much needed oxygen into our blood stream.
- Liver - The liver performs all sorts of vital functions in our bodies from helping us to break down food in digestion to ridding our bodies of toxins.
- Stomach - The stomach holds our food when we first eat it and secretes enzymes that help to break down our food before it goes to the small intestine.
- Kidneys - The kidneys help to keep our bodies clean from toxins and other waste products. Without our kidneys our blood would quickly become poisoned.
- Heart - The heart is considered by many to be the center of life. Having a healthy heart helps to keep the rest of the organs and body healthy as well.
- Skin - The skin is a major organ that covers our entire body. It also provides feedback to the brain through the sense of touch.
- Some organs are called hollow organs because they have an empty tube or pouch. Examples of hollow organs include the stomach, intestine, and the heart.
- The eye is an organ that is generally considered part of the nervous system.
- Other organ systems in the human body include the immune system and the lymphatic system.
- The small intestine is actually much longer than the large intestine.
- Some scientists say that the liver performs as many as 500 different functions.
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